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Atoms and Elements 4 Chapter Overview
Chapter 4 brings us from the earliest recorded ideas on atomic theory over 2000 years ago up to the present day. This chapter serves as a historical timeline giving the students a better understanding of the origins of the facts that we assert. The origin of current atomic theory is presented and the students vocabulary is again extended.
4.1 Experiencing Atoms at Tiburon A. Atoms are very small
B. Atoms make up all matter
C. ~91 different naturally occurring elements 4.2 Indivisible: The Atomic Theory
Learning Objective: Recognize that all matter is composed of atoms. A. Democritus (~400 BC)
B. Dalton (early 1800s)
1. Each element is composed of tiny indestructible particles called atoms
2. All atoms of a given element have the same mass and other properties that
distinguish them from atoms of other elements
3. Atoms combine in simple, whole-number ratios to form compounds
4.3 The Nuclear Atom
Learning Objective: Explain how the experiments of Thomson and Rutherford led to the development of the nuclear theory of the atom.
A. Positive and negative charges (Thomson)
B. Mostly empty space (Rutherford)
C. Current nuclear theory of the atom
1. Most of the atoms mass and all of its positive charge are contained in the nucleus
2. Most of the atom is empty space with small fast moving electrons
3. Number of protons = number of electrons in neutral atoms 4.4 The Properties of Protons, Neutrons, and Electrons
Learning Objective: Describe the respective properties and charges of electrons, neutrons, and protons.
A. Masses expressed in atomic mass units (amu)
B. Protons and neutrons about 2000 times more massive than electrons
C. Nature of electrical charge
1. Electrical charge is a fundamental property of protons and electrons 2. Species of opposite electric charge are attracted to each other
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3. Species of the same electric charge repel each other
4. Species of opposite electric charge cancel to make a neutral atom 4.5 Elements: Defined by Their Number of Protons
Learning Objective: Determine the atomic symbol and atomic number for an element using the periodic table.
A. Identity of atom comes from the number of protons
B. Atomic number (Z) = number of protons
C. Chemical symbol is a shorthand notation of chemical name 1. C = carbon
2. O = oxygen
3. Co = cobalt
4.6 Looking for Patterns: The Periodic Law and the Periodic Table
Learning Objective: Use the periodic table to classify elements by group. A. Mendeleev (1834 1907)
B. Periodic law
E. Metalloids, also known as semiconductors F. Individual group names
1. Group 1 alkali metals
2. Group 2 alkaline earth metals 3. Group 7 halogens
4. Group 8 noble gases
4.7 Ions: Losing and Gaining Electrons
Learning Objective: Determine ion charge from numbers of protons and electrons. Learning Objective: Determine the number of protons and electrons in an ion.
A. If an atom has different numbers of protons and electrons it is an ion
B. Cation = positive ion
C. Anion = negative ion
D. Periodic trends
1. Group 1: +1 ion only
2. Group 2: +2 ion only
3. Group 7: usually 1 ion
4.8 Isotopes: When the Number of Neutrons Varies
Learning Objective: Determine atomic numbers, mass numbers, and isotope symbols for an isotope.
Learning Objective: Determine number of protons and neutrons from isotope symbols. A. Isotopes have the same chemical properties, but different masses
B. Some isotopes are more prevalent than others
C. Chemical symbol with mass number indicates which isotope
D. Some elements have many isotopes, some very few
4.9 Atomic Mass: The Average Mass of an Elements Atoms
Learning Objective: Calculate atomic mass from percent natural abundances and isotopic masses.
A. Value on periodic table represents average mass of all isotopes
B. No chlorine atom weighs exactly 35.453 amu
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Chemical Principle Teaching Ideas
The Atomic Theory
Many students believe that we have completely understood current atomic theory for
centuries. They do not understand that the concepts we now hold as truth became mainstream 200 years ago, with many changes occurring since. Providing a brief history of atomic theory, starting with Plato and Aristotles belief that the four elements; air, water, earth, and fire were the ingredients of all matter gives students a historical perspective.
Discovery of the Atoms Nucleus
Demonstrations of the rudimentary experiments that revolutionized atomic theory will go
a long way toward making students understand that chemistry is an experimental science and that most of what we learn was discovered through pure experimentation.
Most students understand the concept of electrical charge, but a simple demonstration of
static electricity will reinforce the idea.
The Periodic Table
The periodic table can be the best exam cheat sheet a student could ever use. By
understanding the layout of the table, many trends and quite a lot of information can be extracted. Mentioning briefly the things that have periodic trends will also reinforce the periodic law in their minds.
Atomic Number, Ions, and Isotopes
Emphasize that all atoms having the same number of protons behave the same chemically
and only differ in their mass and then only if they are different isotopes. A real world example is a pile of paper clips of various shapes, sizes, and colors. They differ in observable properties, but all behave the same when they react as they all hold paper. A similar example can be made with cork stoppers of different sizes.
Skill Builder Solutions
4.1. a. Located in Group 1A, sodium is atom #11.
b. Located in Group 8B, nickel is element #28.
c. Located in Group 5A, phosphorus is element #15. d. Located in Group 5B, tantalum is element #73.
4.2. a. Sulfur is in Group 6A and is a nonmetal.
b. Chlorine is in Group 7A and is a nonmetal.
c. Titanium is in Group 4B and is a metal.
d. Antimony is considered a metalloid in Group 5A.
4.3. a. Group 1A is called the alkali metal group. b. Group 3A has no special name.
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c. Iodine is in the Group 7A, also known as the halogen group. d. Argon is in Group 8A, also known as the noble gases.
4.4. a. Nickel has 28 protons, so the net charge is 28 26 = +2.
b. Bromine has 35 protons, so the ion charge = 35 36 = -1.
c. Phosphorus has 15 protons, so the ion charge = 15 18 = -3.
4.5. All sulfur atoms have 16 protons. If the net charge is 2, that means there are 2 more electrons than protons in the atom, so there are 16 + 2 = 18 electrons.
4.6. Potassium tends to lose one electron to form a +1 ion, and selenium tends to gain two electrons to form a 2 ion.
4.7. Chlorine atoms all have 17 protons so Z = 17, and since there are 18 neutrons, the mass
number is 35. Therefore, the chemical symbol is 35 Cl . 17
4.8. All potassium atoms have 19 protons, so there are 39 19 = 20 neutrons.
4.9. 78.99 (23.99 amu) + 10.00 (24.99 amu) + 11.01 (25.98 amu) = 24.31 amu
100 100 100
If an atom has a net charge of zero, what could you conclude about the relative number of electrons and protons? Explain.
Rutherfords gold foil experiment showed that practically all the mass is concentrated in a very small location called the nucleus. Which particles must be in the nucleus?
A mad scientist proposes that Type 2 carbon has more protons. How would you respond? How many electrons would you need to weigh the same as one proton?
Describe the relationship between the name of an element and its symbol.
Guided Inquiry Ideas
Below are a few example questions that students answer in the guided inquiry activities provided in the Guided Activity Workbook.
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